Diverse polymorphism within a short coding region of the human aldehyde dehydrogenase-5 (ALDH5) gene

Behavioral consequences of the downstream products of ethanol metabolism involved in alcohol use disorder

Research concerning Alcohol Use Disorder (AUD) has previously focused primarily on either the behavioral or chemical consequences experienced following ethanol intake, but these areas of research have rarely been considered in tandem. Compared with other drugs of abuse, ethanol has been shown to have a unique metabolic pathway once it enters the body, which leads to the formation of downstream metabolites which can go on to form biologically active products. These metabolites can mediate a variety of behavioral responses that are commonly observed with AUD, such as ethanol intake, reinforcement, and vulnerability to relapse. The following review considers the preclinical and chemical research implicating these downstream products in AUD and proposes a chemobehavioral model of AUD.

Genetic variants in ALDH1B1 and alcohol dependence risk in a British and Irish population: A bioinformatic and genetic study

Alcohol is metabolized in the liver via the enzymes alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Polymorphisms in the genes encoding these enzymes, which are common in East Asian populations, can alter enzyme kinetics and hence the risk of alcohol dependence and its sequelae. One of the most important genetic variants, in this regards, is the single nucleotide polymorphism (SNP) rs671 in ALDH2, the gene encoding the primary acetaldehyde metabolizing enzyme ALDH2. However, the protective allele of rs671 is absent in most Europeans although ALDH1B1, which shares significant sequence homology with ALDH2, contains several, potentially functional, missense SNPs that do occur in European populations. The aims of this study were: (i) to use bioinformatic techniques to characterize the possible effects of selected variants in ALDH1B1 on protein structure and function; and, (ii) to genotype three missense and one stop-gain, protein-altering, non-synonymous SNPs in 1478 alcohol dependent cases and 1254 controls of matched British and Irish ancestry. No significant allelic associations were observed between the three missense SNPs and alcohol dependence risk. The minor allele frequency of rs142427338 (Gln378Ter) was higher in alcohol dependent cases than in controls (allelic P = 0.19, OR = 2.98, [0.62–14.37]) but as this SNP is very rare the study was likely underpowered to detect an association with alcohol dependence risk. This potential association will needs to be further evaluated in other large, independent European populations.

Human ALDH1B1 polymorphisms may affect the metabolism of acetaldehyde and all-trans retinaldehyde--in vitro studies and computational modeling

PURPOSE

To elucidate additional substrate specificities of ALDH1B1 and determine the effect that human ALDH1B1 polymorphisms will have on substrate specificity.

METHODS

Computational-based molecular modeling was used to predict the binding of the substrates propionaldehyde, 4-hydroxynonenal, nitroglycerin, and all-trans retinaldehyde to ALDH1B1. Based on positive in silico results, the capacity of purified human recombinant ALDH1B1 to metabolize nitroglycerin and all-trans retinaldehyde was explored. Additionally, metabolism of 4-HNE by ALDH1B1 was revisited. Databases queried to find human polymorphisms of ALDH1B1 identified three major variants: ALDH1B1*2 (A86V), ALDH1B1*3 (L107R), and ALDH1B1*5 (M253V). Computational modeling was used to predict the binding of substrates and of cofactor (NAD(+)) to the variants. These human polymorphisms were created and expressed in a bacterial system and specific activity was determined.

RESULTS

ALDH1B1 metabolizes (and appears to be inhibited by) nitroglycerin and has favorable kinetics for the metabolism of all-trans retinaldehyde. ALDH1B1 metabolizes 4-HNE with higher apparent affinity than previously described, but with low throughput. Recombinant ALDH1B1*2 is catalytically inactive, whereas both ALDH1B1*3 and ALDH1B1*5 are catalytically active. Modeling indicated that the lack of activity in ALDH1B1*2 is likely due to poor NAD(+) binding. Modeling also suggests that ALDH1B1*3 may be less able to metabolize all-trans retinaldehyde and that ALDH1B1*5 may bind NAD(+) poorly.

CONCLUSIONS

ALDH1B1 metabolizes nitroglycerin and all-trans-retinaldehyde. One of the three human polymorphisms, ALDH1B1*2, is catalytically inactive, likely due to poor NAD(+) binding. Expression of this variant may affect ALDH1B1-dependent metabolic functions in stem cells and ethanol metabolism.

Genetic variation in alcohol metabolizing enzymes among Inuit and its relation to drinking patterns

BACKGROUND

Variation in genes involved in alcohol metabolism is associated with drinking patterns worldwide. We compared variation in these genes among the Inuit with published results from the general population of Denmark and, due to the Asian ancestry of the Inuit, with Han Chinese. We analyzed the association between gene variations and drinking patterns among the Inuit.

METHODS

We genotyped 4162 Inuit participants from two population health surveys. Information on drinking patterns was available for 3560. Seven single nucleotide polymorphisms (SNPs) were examined: ADH1B arg48his, ADH1C ile350val, ADH1C arg272gln, ALDH2 glu504lys, ALDH2 5'-UTR A-357G, ALDH1B1 ala86val and ALDH1B1 arg107leu.

RESULTS

The allele distribution differed significantly between Inuit and the general population of Denmark. A protective effect on heavy drinking was found for the TT genotype of the ALDH1B1 arg107leu SNP (OR=0.59; 95% CI 0.37-0.92), present in 3% of pure Inuit and 37% of Danes. The ADH1C GG genotype was associated with heavy drinking and a positive CAGE test (OR 1.34; 95% CI 1.05-1.72). It was present in 27% of Inuit and 18% of Danes. The Asian genotype pattern with a high frequency of the ADH1B A allele and an ALDH2 gene coding for an inactive enzyme was not present in Greenland.

CONCLUSIONS

ADH1C and ALDH1B1 arg107leu SNPs play a role in the shaping of drinking patterns among the Inuit in Greenland. A low frequency of the ALDH1B1 arg107leu TT genotype compared with the general population in Denmark deserves further study. This genotype was protective of heavy drinking among the Inuit.

The association of alcohol and alcohol metabolizing gene variants with diabetes and coronary heart disease risk factors in a white population

BACKGROUND

Epidemiological studies have shown a J- or U-shaped relation between alcohol and type 2 diabetes and coronary heart disease (CHD). The underlying mechanisms are not clear. The aim was to examine the association between alcohol intake and diabetes and intermediate CHD risk factors in relation to selected ADH and ALDH gene variants.

METHODOLOGY/PRINCIPAL FINDINGS

Cross-sectional study including 6,405 Northern European men and women aged 30-60 years from the general population of Copenhagen, Denmark. Data were collected with self-administered questionnaires, a physical examination, a 2 hour oral glucose tolerance test, and various blood tests. J shaped associations were observed between alcohol and diabetes, metabolic syndrome (MS), systolic and diastolic blood pressure, triglyceride, total cholesterol, and total homocysteine. Positive associations were observed with insulin sensitivity and HDL cholesterol, and a negative association with insulin release. Only a few of the selected ADH and ALDH gene variants was observed to have an effect. The ADH1c (rs1693482) fast metabolizing CC genotype was associated with an increased risk of impaired glucose tolerance (IGT)/diabetes compared to the CT and TT genotypes. Significant interactions were observed between alcohol and ADH1b (rs1229984) with respect to LDL and between alcohol and ALDH2 (rs886205) with respect to IGT/diabetes.

CONCLUSIONS/SIGNIFICANCE

The selected ADH and ALDH gene variants had only minor effects, and did not seem to markedly modify the health effects of alcohol drinking. The observed statistical significant associations would not be significant, if corrected for multiple testing.

Genetic determinants of both ethanol and acetaldehyde metabolism influence alcohol hypersensitivity and drinking behaviour among Scandinavians

BACKGROUND

Although hypersensitivity reactions following intake of alcoholic drinks are common in Caucasians, the underlying mechanisms and clinical significance are not known. In contrast, in Asians, alcohol-induced asthma and flushing have been shown to be because of a single nucleotide polymorphism (SNP), the acetaldehyde dehydrogenase 2 (ALDH2) 487lys, causing decreased acetaldehyde (the metabolite of ethanol) metabolism and high levels of histamine. However, the ALDH2 487lys is absent in Caucasians.

OBJECTIVES

To investigate the genetic determinants of self-reported alcohol-induced hypersensitivity reactions in Caucasians.

METHODS

The study included two population-based studies of 1216 and 6784 adults living in Copenhagen. Assessment of alcohol consumption and hypersensitivity reactions (in a subgroup) was performed by a questionnaire and was related to common SNPs of genes encoding alcohol dehydrogenases (ADHs) and ALDHs.

RESULTS

In both populations, alcohol drinkers with a genetically determined fast metabolism of ethanol (the A allele of the ADH1b rs1229984) had an increased risk of alcohol-induced hypersensitivity reactions (odds ratio AA/AG vs. GG in combined populations: 1.82, 95% CI 1.04-3.17). In both populations, a common SNP encoding ALDH1b1 (rs2228093) was found to be significantly associated with alcohol-induced hypersensitivity (odds ratio TT vs. CC in combined populations: 2.53, 95% CI 1.31-4.90).

CONCLUSIONS

Our data support that alcohol sensitivity in Caucasians is genetically determined and suggest that a histamine-releasing effect of acetaldehyde represents a plausible biological mechanism. Furthermore, we present the first report of a clinically significant SNP within the acetaldehyde-metabolizing system in a Caucasian population.

The association of ADH and ALDH gene variants with alcohol drinking habits and cardiovascular disease risk factors

BACKGROUND

Genetic variation in ethanol metabolism may have an influence on both alcohol drinking habits and the susceptibility to health effects of alcohol drinking. Such influences are likely to bias exposure-disease associations in epidemiologic studies of health effects of alcohol drinking. In a Caucasian population, we examined the association of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) genetic variants with alcohol drinking habits, biomarkers of alcohol exposure, and risk factors for cardiovascular disease.

METHODS

The study population consisted of 1,216 Danish men and women aged 15-77 years participating in a health examination in 1998. The health examination included a self-administered questionnaire (alcohol drinking habits), a physical examination (blood pressure), and various blood tests [alanine aminotransferase (ALAT), erythrocyte mean corpuscular volume (E-MCV), and lipids]. ADH and ALDH gene variants were determined by standard techniques. Data were analyzed by regression analyses adjusted for relevant confounders.

RESULTS

Self-reported alcohol drinking was significantly associated with increasing levels of ALAT, E-MCV, high-density lipoprotein cholesterol, and blood pressure. The ALDH1b ala69val variant was associated with nondrinking and total alcohol intake. The ALDH2 promoter variant was associated with binge-drinking, and the ALDH1b1 ala69val polymorphism was associated with diastolic blood pressure. We did not find any statistically significant interactions between any of the gene variants and alcohol consumption in relation to the various outcomes.

CONCLUSIONS

In this Caucasian population sample, we found evidence to support that genetic variation in ethanol metabolism may influence drinking habits, but no statistically significant gene-environment interactions. More large-scale epidemiologic studies are needed to confirm theses results and to further investigate genetic susceptibility to the effects of alcohol drinking.

Genetic markers of alcohol abuse

In this paper, we review the current status of genetic markers for the development of alcohol abuse. Family, twin, half-sibling and adoption studies of alcoholic subjects suggest that the heritability of liability to alcoholism is at least 50%. These findings have fuelled intensive investigation in the fields of neurology, biochemistry, genetics and molecular biology aimed at the identification of markers for the risk of alcoholism. The most promising of these are discussed in detail. Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) polymorphisms, specifically the ADH3*1, ADH2*2, and ALDH2*2 genotypes appear to confer a protective effect against alcoholism, most notably in Oriental subjects. Caucasian alcohol abusers and their first-degree relatives exhibit depressed platelet monoamine oxidase activity, the degree of which is greater in Type II than Type I alcoholics. Electrophysiological characteristics of alcoholics and those at risk for developing alcoholism have also been identified, including the reduced amplitude of the event-related brain potential and, after ethanol ingestion, characteristic EEG alpha-wave activity. Lower platelet adenylate cyclase activity is seen in alcoholics compared to controls, presumably as a result of over-expression of an inhibitory G-protein. Markers related to other signal transduction pathways of the central nervous system including the serotoninergic, muscarinic and dopaminergic systems are also discussed. In this group of markers, the putative association between the inheritance of the AI allele of the D2 dopamine receptor and the susceptibility to alcoholism provides the most dramatic illustration of the challenges presently existing in this field of scientific investigation. Current limitations in the definition, diagnosis and classification of alcoholism, the confounding influences of race and gender on association studies, as well as the statistical approach of linkage studies are discussed as they relate to the endeavor to uncover valid genetic markers for the risk of alcoholism.

Alcohol and acetaldehyde dehydrogenase gene polymorphism and alcoholism

Inherited variations in alcohol and aldehyde dehydrogenases, the principal enzymes of ethanol metabolism, have been implicated in determining susceptibility to alcoholism and alcohol-related organ damage. An association between an RFLP for the alcohol dehydrogenase-2 (ADH2) gene and alcohol-induced liver damage was demonstrated in a Caucasian population. Genotyping studies revealed an increase in the ADH3(2) allele in patients with alcohol-induced cirrhosis. PCR studies of the ALDH5 gene have demonstrated diverse polymorphism within a short segment of its coding region, with marked inter-racial variation in allele frequencies. In addition, the Caucasian alcohol-induced flushing reaction has been characterised and its relationship with phenotypic polymorphism of ALDH1 examined.